Important objects of the present invention are to provide an improved switch of the above type characterized by simplified low cost design and construction and that is light in weight, compact, highly reliable, and capable of economical manufacture by automated mass production procedures; to provide such a switch contained within an improved cylindrical plastic housing that minimizes the possibility of shorting to ground and effectively seals the electrical contacts from the atmosphere and corrosion; to provide such a switch having improved contact elements including a spherical contact member or metallic ball movable by gravity within a cylindrical electrical conductor secured coaxially to the cylindrical housing such that operation of the switch is assured regardless of the rotational position of the housing axis; and to provide an improved economical and automated method of manufacturing such a switch wherein dimensional tolerances between the external electrical contacts are closely maintained without recourse to precise and expensively maintained dimensions for the component parts.
Among the problems involved in the substitution of such a gravity switch for a mercury switch are ball sticking or a welding effect and high millivolt drop across the electrical contacts. Ball sticking or welding of the ball to the contacts at the "on" or a closed circuit position impairs gravity induced movement of the ball to the "off" or open circuit condition. Also a comparatively high voltage drop between the ball and the switch contacts at the closed circuit condition results in loss of electrical power, or luminous intensity when the switch is employed with an electric light.
The above problems are overcome in accordance with the present invention by providing means for significantly increasing the contact pressure between the ball and the switch contact elements. Inasmuch as the overall switch dimensions are severely limited by the requirement of maintaining interchangeability with customarily employed mercury switches, the design of the ball switch is critical.
Other objects accordingly are to provide an improved switch design which, without increasing the external dimensions of the switch, enables use of a larger diameter ball contact element of correspondingly greater weight, which in turn has been found to reduce the voltage drop across the ball contacts materially when the switch is tilted to the "on" position. In consequence, a comparatively costly lead ball, which has been heretofore preferred in small switches because of its high specific gravity, can be replaced by a larger, heavier, and less costly brass ball which reduces voltage loss across the contacts and likewise the welding effect and enables efficient operation of the switch with larger current flow than heretofore. By suitably plating the ball element, as for example with zinc, tin, or cadmium, and by sonic cleaning of the contact elements immediately prior to their assembly, the welding effect and consequent ball sticking are further reduced and optimum electrical conductivity through the switch is achieved.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.